It is known from DE 44 35 322 A1 subsequently to flange an exhaust gas housing onto the housing of a gas turbine. The exhaust gas housing consists essentially of a hub-side annular inner part and of an annular outer part which are connected to one another via a plurality of radial carrying ribs arranged uniformly over the circumference. The outlet-side mounting of the turbine shaft is arranged in the cavity within the annular inner part. For sealing off the mounting against hot exhaust gases, normally shaft seals are used and barrier air is injected. In addition, ambient air can be introduced into the bearing space via a fan and is transported outward via the shaft seal and through passages in the exhaust gas diffuser. This cooling air may also be used for cooling the annular inner part of the exhaust gas housing. For this purpose, cooling ducts are arranged in the inner part, which are located at the foot of the carrying ribs and are fed with cooling air via bores.
EP 1 108 858 A2 discloses an exhaust gas housing which, for the protection of the bearing of a gas turbine, has a special double-walled bearing housing, in order to protect the bearing of the turbine reliably from the exhaust gases. This special bearing housing is acted upon, in a way not explained in any more detail, by cooling air which is already used for the exhaust gas housing and which is likewise introduced via an external fan.
In the event of insufficient protection for the exhaust gas housing and of the associated carrying structure, in particular the carrying ribs, from the high thermal stresses caused by the hot exhaust gases, problems may arise with material creeping actions, thus leading to material defects. In the case of uneven exhaust gas temperature profiles, there may be a deformation of the carrying structure and consequently a deflection of the rotor out of center, which may lead to a failure of the thermal engine.